Multi-push (MP) acoustic radiation force (ARF) ultrasound for assessing tissue viscoelasticity, in vivo.

Acoustic radiation force (ARF) ultrasound is a method of elastographic imaging in which micron-scale tissue displacements, induced and tracked by ultrasound, reflect clinically relevant tissue mechanical properties. Our laboratory has recently shown that tissue viscoelasticity is assessed using the novel Multi-Push (MP) ARF method. MP ARF applies the Voigt model for viscoelastic materials and compares the displacements achieved by successive ARF excitations to qualitatively or quantitatively represent the relaxation time for constant stress, which is a direct descriptor of the viscoelastic response of the tissue. We have demonstrated MP ARF in custom viscoelastic tissue mimicking materials and implemented the method in vivo in canine muscle and human renal allografts, with strong spatial correlation between MP ARF findings and histochemical features and previously reported mechanical changes with renal disease. These data support that noninvasive MP ARF is capable of clinically relevant assessment of tissue viscoelastic properties.